"While the results of this study may appear contradictory or somewhat confusing, the take-home message is that overall, obesity causes more harm than good," said Dr. Richard Libman, who reviewed the findings. He's vice chair of neurology at Long Island Jewish Medical Center in New Hyde Park, N.Y.

Specifically, the British study of more than 1.3 million women found that overweight and obese women were more likely to suffer an ischemic stroke, where blood flow is blocked to the brain. According to the American Stroke Association, it is by far the leading form of stroke, accounting for about 87 percent of cases.

The study found that overweight and obese women were somewhat less likely to have a bleeding, or hemorrhagic, stroke, which comprises about 13 percent of cases.

The study was led by Gillian Reeves of the University of Oxford in England. Her team tracked the 12-year health history of British women who averaged 57 years of age.

During that time, rates of ischemic (the blockage type) stroke were 1 percent among obese women and 0.7 percent among women with a healthy weight.

On the other hand, rates of bleeding stroke were 0.4 percent among obese women and 0.5 percent among women with a healthy weight.

The study was published in the Sept. 7 online issue of the journal Neurology.

"Our findings add to the growing body of evidence that different types of stroke have different risk profiles," Reeves said in a journal news release.

Libman called the study "well done," noting that prior studies have also found that race plays a role in the relationship between weight and stroke risk.

"For Europeans in general, consisting mostly of whites, the risk of stroke due to blockage increases with greater obesity, while the risk of stroke due to bleeding decreases with greater obesity," he said. However, "in Asians, the risk of both types of stroke seems to increase with obesity."

And just because excess weight may confer a tiny benefit in lowering bleeding stroke risk, that's no reason to pile on the pounds, Libman said.

"As weight increases, the risk of having any type of stroke outweighs any apparent benefit of increasing obesity on the risk of stroke due to bleeding," he said.

Dr. Mitchell Roslin is chief of obesity surgery at Lenox Hill Hospital in New York City. He said that, as in many health issues, "not every obese person has the same risk."

But Roslin noted that obesity is strongly tied to heart risk factors such as diabetes and high blood cholesterol levels.